Most of the cruisers that I know in the Caribbean use www.WindGuru.cz for forecasts - including myself. It gives excellent short-term wind and waves and that is sufficient for all Caribbean passages. I use a number of sites including NOAA for "real" weather when I want something more in-depth.

WindGuru. I really like their graphic display. It packs a lot of info into one chart (average wind speed/direction, gusts, cloud cover, pressure, rain...all in one graphic).

Wide Area

Multiple tools. Like many, I download GRIBs. I also use NOAA RadioFax charts a lot. Be aware of the limitations of GRIBs (raw model output with no pro human review/revision, do not show fronts and other significant features, ...). Many mistakenly use them almost exclusively and do not compensate for their short comings.

Historic Trends

Pilot Charts. I still use Pilot Charts, but as Stu posted there are more up to date tools/data becoming available.

And a step beyond your question:

Weather Routing. I do my own weather routing and also weather route for friends when Im ashore. I use all the above tools plus SailGRIB WR (which uses GRIB data for both winds and currents). Just finished routing for friends on a non-stop run from Florida to Guatemala.

Their trip makes for a great example of a short coming of GRIBs. They downloaded GRIBs, looked at wide area systemic winds of about 15 knots and were all ready to go for it...what the basic GRIB view did not show them was large powerful cold front crossing the Gulf of Mexico that would have crossed their route in a few days. The surrounding systemic winds were not forecast to be much more that 20 knots, but....the conditions on the frontal boundary were forecast to be VERY unstable (CAPE index near 4,000 in some areas!). Such highly unstable air can result in extremely bad localized weather (which most forecast options won't show). I convinced them to delay their departure...the frontal crossing brought some really ugly weather over their location...they left on the front's trailing edge and made the entire run from FL to Guatemala in easy favorable conditions...sure beats the butt kicking they would have gotten on their original GRIB only based plans.